I was wondering who owns the copyright of the sourcecode if you port an opensource project from one language to another. Is there a clear answer, or does it 'depend'?

edit: I'm aware that a license choice is bound to the license the original sourcecode is released under, but I'm strictly wondering about the IP/copyright. As in, could I change copyright (c) 2011 original author to copyright (c) 2011 my name in all source files.

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In general, no. Translations are typically considered to be derived works, so what you'd be doing is adding your copyright notices, not changing or removing the old ones. The exception would be a "clean room" implementation, in which one team analyzes the app to make a very detailed spec, and another team builds a new app from the spec. (A variant is to just write a new program that's compatible with the old documentation.) For details, consult a lawyer.

You seem a little confused about licenses vs. copyrights. F/OSS licenses are valid only because of copyright. Therefore, if you have to keep the license, you have to keep the copyright.

Besides, removing copyright notices is a scummy thing to do. F/OSS is largely a reputation economy, and so by claiming somebody else's work as your own, you are stealing reputation from them.

[edit]To be pedantic, if you wrote it, you own the copyright to it. You may, however, not be able to distribute your new project to anyone without a licence from the copyright owner of the work your work is derived from.

We now return you to your regularly scheduled coverage of whether or not your work is derivative:[/edit]

It depends on how much you look at the original code. At one end of the spectrum, if you slavishly translate each line of the old code into the new language, it's a derivative work, and you must comply with the licence of the original project.

On the other hand, it is possible to determine the requirements for the new project purely by examining it in use (without looking at the code). If you do that, then write the a new project from scratch which fulfils these requirements, it has nothing to do with the original project, and the copyright is entirely yours to do what you wish with. ReactOS did/is doing this with Windows.

Of course, in the real world, there is a whole spectrum of greys in between those two extremes. IANAL, but you should tend to err on the side of complying with the licence. The great thing about free software is that looking at the source code and modifying it (or re-writing it) is entirely allowed, although you still need to comply with any restrictions the licence places on derivative works.

I am no lawyer, however if not legally, at least morally, the port is no differenct to any other modification of the code. The ported copy is still based on the original work, hence you would be bound by the license agreement from the original work.